Previously, the genus Manta was considered monotypic by most authors. The genus was re-evaluated and two species, Reef Manta Ray (Manta alfredi) and Giant Manta Ray (Manta birostris), were identified (Marshall et al. 2009). Genetic evidence further confirms the existence of two separate species (Kashiwagi et al. 2008a, Ito and Kashiwagi 2010). Both species have worldwide distributions. The two Manta species are sympatric in some locations and allopatric in others (Kashiwagi et al. 2011).

Reports are often mixed as the splitting of the genus occurred very recently (2009). Historical reports can often be confusing as well without adequate descriptions or photographs. Care should be taken when using reports or accounts of the Reef Manta Ray that they are not referring to the Giant Manta Ray (or vice versa).

Melanistic (black) and leucistic (white) colour morphs occur in both species of Manta (Marshall et al. 2009). Variant colour morphs often contribute an added degree of confusion when attempting to visually discriminate between species of Manta in the field or in photographs, especially when close examination is not possible. It should be noted that these colour morphs could be a possible source of error, resulting in mis-identifications in past or future studies or surveys of distribution.

Manta rays are often confused with the devil rays of the genus Mobula, and care should be used to ensure reports of mantas are actually of Manta and not this sister genus.

Justification:
The Reef Manta Ray (Manta alfredi) has a circumtropical and sub-tropical distribution, existing in the Pacific, Atlantic and Indian Oceans. Within this broad range, however, actual populations appear to be sparsely distributed and highly fragmented. This is likely due to the specific resource and habitat needs of this species.

Overall population size is unknown, but subpopulations appear, in most cases, to be small (about 100–2,000 individuals). A proportion of the individuals in some populations undertake significant coastal migrations, crossing national boundaries or entering into international waters. Although the degree of interchange of individuals between subpopulations is unclear, it is assumed to be low as there are currently no data that support such interchange despite active investigations. As such, declines in small subpopulations may eventually result in regional depletions or extirpation with the reduced possibility of successful recolonization. To aggravate this situation, this species has a very conservative life history with an extremely low reproductive output. In the wild, females bear on average a single pup every 2–3 years. These biological constraints would actively contribute to its slow or lack of recovery from population reductions.

The rate of population reduction appears to be high in several regions, up to as much as 80% over the last three generations (approximately 75 years), and globally a decline of 30% is strongly suspected. Currently this species has a high value in international trade (its gill rakers are used in Chinese medicines) and directed fisheries exist that target this species in what is certain to be unsustainable numbers. Artisanal fisheries also exist that target this species for food. Individuals are also taken as bycatch in everything from large-scale fisheries to shark control programs/bather protection nets. As a result of sustained pressure from fishing (both directed and bycatch) certain monitored subpopulations appear to have been depleted, such as in Indonesia. Of particular concern is the targeting of this species at critical habitats or well-known aggregation sites where, with relatively high catch-per-unit effort, numerous individuals can be targeted simultaneously or with relative ease.

Dive tourism involving this species is a growing industry and it has been demonstrated that sustainable tourism significantly enhances the economic value of such species in comparison to short-term returns from fishing. Tourism related industries can also negatively impact individual behaviour, entire populations and critical habitat for this species, thus the responsible development of these industries is recommended.

This species has a circumglobal range in tropical and sub-tropical waters. This species is widespread in the Indian Ocean, with images and sightings of the Reef Manta Ray from the Sinai Peninsula in the Red Sea to Durban, South Africa in the Western Indian Ocean, and from Thailand to waters off Perth, Western Australia in the Eastern Indian Ocean. In the eastern and south Pacific, the Reef Manta Ray occurs from southern Honshu and islands on Ryukyu Arc, Japan in the north to the Solitary Islands (New South Wales), Australia in the south and is sighted as far east as French Polynesia south of the equator and the Hawaiian Islands north of the equator. Two verified reports and photographs of the Reef Manta Ray from the North Atlantic off the Canary Islands and the Cape Verde Islands, and historical reports and photos of the Reef Manta Ray off the coast of Senegal in northwest Africa (Cadenat 1958) are the only evidence of populations of the Reef Manta Ray in Atlantic waters.

The Reef Manta Ray is often encountered in large numbers when feeding and individuals are sometimes seen travelling in schools. Overall, divers encounter the Reef Manta Ray with far greater frequency than the Giant Manta Ray. Due to the global nature of their individual distributions, absolute population sizes will always be difficult to assess. Currently, the overall total global population sizes of both these species are unknown, but some regional populations have been estimated.

Subpopulations of the Reef Manta Ray appear, in most cases, to be small (less than 1,000 individuals). The degree of interchange of individuals between subpopulations is unclear but is assumed to be low, as there are currently no data that support such interchange, despite active research efforts to investigate this (A. Marshall et al. unpubl. data 2011). Photo-identification studies at aggregation sites in Hawaii (Deakos et al. 2011), Yap (B. Acker pers. comm. 2009), Japan (Ito 1987, Homma et al. 1999, Ito 2000, Kashiwagi et al. 2008b), and the east coast of Australia (M. Bennett and F. McGregor pers. obs. 2011) have produced sighting records of approximately 85 to 400 individuals, despite some being active for many decades. A semi-exhaustive study of Japan-wide photographic records confirmed that the known main aggregation in Yaeyama Islands (300 known individuals since 1977) represents a part of a fairly isolated population (Kashiwagi et al. 2010). Only monitoring programs in Tofo Beach, southern Mozambique (n=630 in April 2011) the Maldivian Islands (n1,500 in early 2010) and Ningaloo in Western Australia (n=530 in early 2010) have registered sightings of more than 500 individuals from a single aggregation site (Kitchen-Wheeler 2010, A. Marshall unpubl. data 2011, F. McGregor unpubl. data 2011, G. Stevens unpubl. data 2011). A mark-recapture population study in southern Mozambique over four years from 2003 to 2007 estimated the local population during that time to be about 800 individuals (Marshall et al. 2011).

Preliminary studies at major aggregation sites suggest resident population sizes are generally small, with some areas having large seasonal influxes. There appears to be a tendency for rays to visit/occupy specific sites of restricted geographical extent, in part for interactions with cleaner organisms, for social and reproductive behaviours, and for feeding (O’Shea et al. 2010). Results also suggest a high degree of separation between subpopulations.

Movement patterns are likely site-specific and correlated with cycles in productivity. Individuals have been documented to make seasonal migrations of several hundred kilometres as well as daily migrations of almost 70 km (A. Marshall et al. unpubl. data 2011). The annual migration range in Japan has been documented to be up to 400 km (Homma et al. 1999, Kashiwagi et al. 2010) and up to 270 km in the Maldives (Kitchen-Wheeler 2010, Anderson et al. 2011, G. Stevens unpubl. data 2011), while along the east coast of Australia, Reef Manta Rays have been documented to travel distances of up to 500 km (Couturier et al. 2011).

Populations are likely to be stable in locations where they receive some level of protection, such as Australia, Hawaii, Japan, the Maldives and Yap, but are likely to be in decline in areas where they are fished, or are under threat from anthropogenic influences e.g., Indonesia (Dewar 2002), Thailand (A. Marshall unpubl. data 2011) and Mozambique (A. Marshall unpubl. data 2011) where encounter rates have dropped significantly over the last five years or anthropogenic mortality has been elevated.

Overall, the rate of population reduction appears to be high in several regions, up to as much as 80% over the last three generations (approximately 75 years), and globally a decline of 30% is strongly suspected.

Historical fisheries data and reported declines in population numbers:

In the Alor region of eastern Indonesia (Lamalera and Lamakera), it is reported that up to 2,400 rays, particularly manta rays and a few species of the genus Mobula, were historically harvested per year. Once a traditional fishery that did not focus primarily on manta rays, in the 1990s demand for manta ray products created a strong export industry in these small islands. As a result, fishing effort increased and the techniques and the equipment improved. Populations of the Reef Manta Ray began to decline in this region suggesting serial depletions. As catches began to decrease, fishermen began to go further afield to find rays to harvest (Dewar 2002).

Barnes (2005) reports that manta rays, including the Reef Manta Ray, have historically been fished by Indigenous villagers in East Flores and Lembata, Indonesia. Catches of mantas were found to vary substantially with 249 individuals being caught in 1959, and only 29 the following year. The highest catch recorded was in 1969 when 360 mantas were caught (this is described as an exceptional year) and the lowest being 10 in 1985. After 1995 the mantas became scarcer and in 1996 no mantas were recorded to be caught. The Indigenous villagers attribute the decline in catch to competition from the Taiwanese commercial fishing vessels that began operating out of the village in the 1990s.

Although there is no solid indication of a total population decrease, observations at an aggregation site at Yaeyama Island, Japan, noted that the number of feeding animals sited at the surface decreased from 50 to 30 in 1970s to at most 15 in 1990s (Homma et al. 1999).

Commonly sighted inshore, but also found around offshore coral reefs, rocky reefs and seamounts. Long-term sighting records of the Reef Manta Ray at established aggregation sites suggest that this species is more resident to tropical waters and may exhibit smaller home ranges, philopatric movement patterns and shorter seasonal migrations than the Giant Manta Ray (Homma et al. 1999, Dewar et al. 2008, Kitchen-Wheeler 2010, Anderson et al. 2011, Deakos et al. 2011, Marshall et al. 2011). Residency is thought to be related to areas of high primary productivity (e.g., upwelling events), which may vary in time and space. Site fidelity to specific areas may also vary by sex and age-class. Seasonal migrations in this species likely correspond with cycles in productivity (Anderson et al. 2011, Couturier et al. 2011).

Individuals in Australia, Japan, the Maldives and Mozambique have been documented making seasonal migrations of several hundred kilometres between well-established aggregation sites, directional movements of up to 500 km, or daily migrations of 70 km (Homma et al. 1999, Kashiwagi et al. 2010, Kitchen-Wheeler 2010, Anderson et al. 2011, Couturier et al. 2011, A. Marshall unpubl. data 2010). While evidence is still being gathered, this is likely to include cross border migration in areas such as Mozambique and South Africa; Egypt, Saudi Arabia and Sudan; and, Australia, Papua New Guinea and Indonesia. Satellite tagging results from northeastern Australia have tracked the Reef Manta Ray for periods of up to 110 days, during which individuals moved up to 780 km in total. During these tracks, individual rays moved into offshore waters up to 190 km from the coast, travelling over waters more than 1,000 m deep. During these tracks individual rays were making periodic dives of up to 300 m (F. Jaine et al. pers. comm. 2011). However, in Hawaii, the Reef Manta Ray exhibits more limited movements, with no documented movement between islands 48 km apart despite extensive photo-identification and acoustic telemetry research (Deakos et al. 2011).

The Reef Manta Ray appears to be a relatively long-lived species. Although the actual longevity of the species remains unknown, photographic databases have re-sighted individuals up to a 30 year period (Ito 2000, Kashiwagi et al. 2010, G. Stevens unpubl. data 2010, T. Kashiwagi and T. Ito unpubl. data 2011). Natural mortality is thought to be low (other than in juveniles), although limited predation from large sharks and Orcas does occur (Visser and Bonoccorso 2003, Marshall and Bennett 2010b).

Generation time is suspected to be 25 years based on conservative estimates of life history parameters. Female mantas are thought to mature at 8–10 years of age and longevity is estimated to be at least 40 years. Generation time is the average age of adults which can be approximated as halfway between age at first maturity and maximum age. Thus female mantas may be actively breeding for 30 years and the age at which 50% of total reproductive output is achieved would be approximately 24–25 years.

The Reef Manta Ray has very low fecundity. The production of a single pup appears to be the normal situation for these rays, although two pups are conceived on occasion (Marshall et al. 2008, Marshall and Bennett 2010a). In southern Mozambique, the Reef Manta Ray gives birth in the austral summer period after a gestation period of approximately one year (Marshall and Bennett 2010a). Reproductive periodicity in the Reef Manta Ray is commonly biennial (Deakos 2010a, Kitchen-Wheeler 2010, Marshall and Bennett 2010a) or longer (Ito 2000, G. Stevens unpubl. data) in the wild, but this species has an annual ovulatory cycle (Marshall and Bennett 2010a) and individuals can and have reproduced annually in the wild (Marshall and Bennett 2010a, M. De Rosemont pers. comm. 2009) and in captivity.

Four captive breeding events and births in consecutive years (2007–2010) have been reported from a pair of Reef Manta Rays in Churaumi Aquarium, Japan. A mating by a male (350 cm disc width (DW), in captivity since May 1992) and a female (420 cm DW, in captivity since August 1998) was observed in a display tank (34 m x 27 m x 10 m) on 8 June 2006. Chasing behaviour by the male started in March and peaked between May and September. This period was reported as “unnaturally” long (Matsumoto et al. 2008). A female (190 cm DW, 68.5 kg) was born 374 days later on 16 June 2007 but died four days later. Attack by the father was suspected as a cause of death. The same couple mated immediately after giving birth and produced a male (182 cm DW) 366 days later on 17 June 2008. The baby was transferred to an open-sea pen. The couple mated on a same day and produced a female (192 cm DW, 70 kg) 372 days later on 24 June 2009. They again mated on the same day and produced a pup (182 cm DW, 66 kg) 367 days later on 26 June 2010 (Anon 2007).

The Reef Manta Ray reaches disc widths of at least 500 cm (Marshall et al. 2009), however, in most populations the average disc widths of mature individuals do not exceed 400 cm. Physical and sexual maturity appear to vary according to region. Males in southern Mozambique mature at approximately 300 cm DW, while females appear to mature at slightly less than 400 cm DW (Marshall and Bennett 2010a). However, males in the Republic of Maldives mature at sizes of 250 cm DW, while the females mature at 300 cm DW (G. Stevens unpubl. data 2011). In Hawaii, the largest female and male were reported at 362 and 303 cm DW, respectively, and size at sexual maturity was estimated at 335 cm DW for females and 280 cm DW for males (Deakos 2010b). Males have been observed mating as early as six years of age (T. Clark unpubl. data 2010). Age at maturity in females is unknown, but is likely to be over eight years of age.

The meat is often sold as food, the liver for local medicine and oil, and branchial filter plates (gill rakers) from Manta and Mobula species fetch high prices in Asia and are used for Chinese medicinal products (Zhongguo yao yong dong wu zhi xie zuo zu bian zhu 1983). Meat from the Reef Manta Ray is also often used for shark bait or attractant. The epidermis of the Reef Manta Ray is also sometimes used for leather products (shoes, wallets, knife handles).

Reef Manta Rays are often caught and transported to aquariums for use in display tanks. The Georgia Aquarium has been housing a single Reef Manta Ray transported from South Africa in their exhibit since 2008. Three aquariums in Japan are keeping the Reef Manta Ray in captivity. Uchida (1994) reported the number of surviving days of individual Reef Manta Rays in captivity in Churaumi Aquarium: 3; 1; 1,943+; 5; 13; 644+; 299+; and 4 since 1978. Currently (September 2010–present) animals captured in 1992, 1998, 2001, 2001, 2005 and 2008 are in captivity (Sato et al. 2010). Four of those are in the display tank. Additionally, two of three surviving captive bred animals are in the exhibition tank. Kaiyukan and Shinagawa Epson Aqua Stadium are exhibiting one animal each. Currently there are no active release programs underway at aquariums where specimens are being housed.

The main threat to both Manta species is fishing, whether targeted or incidental. Manta rays are currently killed or captured by a variety of methods including harpooning, netting and trawling. These rays are easy to target because of their large size, slow swimming speed, aggregative behaviour, predictable habitat use, and lack of human avoidance.

Manta ray products have a high value in international trade markets. Their gill rakers are particularly sought after and are used in Asian medicinal products. This market has resulted in directed fisheries for manta rays, which are currently targeting these rays in unsustainable numbers. Over 1,000 manta rays are caught per year in some areas (Alava et al. 2002, Dewar 2002, White et al. 2006, Anderson et al. 2010). Artisanal fisheries also target both species for food and local products (White et al. 2006, Marshall et al. 2011).

Aside from directed fisheries, manta rays are also incidentally caught as bycatch in both large-scale fisheries and small netting programs such as shark control bather protection nets (Young 2001, C. Rose pers. comm. 2008).

As a result of sustained pressure from fishing (both directed and bycatch) certain monitored subpopulations appear to have been rapidly depleted (e.g., Indonesia and the Philippines; Anon 1997, Alava et al. 2002). Targeting either species of Manta at critical habitats or aggregation sites, where individuals can be caught in large numbers in a short time frame, is a particular threat. Regional populations of both species appear to be small, and localized declines are unlikely to be mitigated by immigration. This situation is exacerbated by the conservative life history of these rays, which constrain their ability to recover from a depleted state.

Cryptic threats such as mooring line entanglement and boat strikes can also wound manta rays, decrease fitness or contribute to unnatural mortality (Marshall and Bennett 2010b, Deakos et al. 2011, F. McGregor pers. obs. 2010). In Maui, Hawaii, 10% of the population has amputated or non-functioning cephalic fins, most likely caused from entanglement in monofilament fishing line (Deakos et al. 2011). Many other threats have been postulated and identified such as habitat degradation, climate change, pollution (from oil spills), ingestion of micro plastics and irresponsible tourism practices.

Dive tourism involving this species is a growing industry and it has been demonstrated that sustainable tourism significantly enhances the economic value of such species in comparison to short-term returns from fishing (Anderson 2002, Anderson et al. 2010). However, rapidly growing tourism (including in-water interactions and recreational boating traffic) if unmanaged, is likely to affect localised use of and visitation rates to critical cleaning and feeding habitats (Osada 2010, Deakos et al. 2011). Their natural behaviour can also be affected by excessive ecotourism (F. McGregor unpubl. data 2010, A. Marshall unpubl. data 2011).

Known directed fisheries:

Reported World CatchManta and devil ray catch increased from 900 tonnes to over 3,300 tonnes between 2000 and 2007 (FAO 2009, Lack and Sant 2009).

Trade-driven FisheriesManta rays, including the Reef Manta Ray, are currently taken in fisheries that have transitioned from bycatch fisheries into directed fisheries, with the birth of a market for manta ray products in Asia.

Mobulid rays are directly fished in large trap nets set in important migratory channels such as in the Tangkoko Nature Reserve in the Manado region of North Sulawesi, Indonesia (Anon 1997). A study of the catch composition in a single year between March 1996 and February 1997 included 1,424 manta rays (unspecified species but likely Reef Manta Ray). While this practice was banned for a while, it started back up illegally in late 1997 and fishing efforts have moved to new unmonitored locations (Anon 1997).

Directed fisheries for manta rays exist in the Alor region of eastern Indonesia. A study of this fishery in 2002 (during the fishing season from May-October) revealed that the traditional whale shark fishery had shifted its focus to manta rays (predominately Reef Manta Ray), which were being harvested for trade to Asian markets, specifically Hong Kong. Estimated annual catch was thought to be 1,500 individuals (range 1,050–2,400 mantas). This was a considerable increase from the traditional 200–300 manta rays taken annually in historical fisheries in the area (Dewar 2002).

Artisanal FisheriesReef Manta Rays are caught in artisanal fisheries in southern Mozambique for consumption. Manta rays are typically harpooned but also caught in nets with motorized boats. Approximately 50 individuals are taken per annum from a 50 km stretch of coastline (Marshall et al. 2011, A. Marshall unpubl. data 2011).

Bycatch fisheriesManta rays are caught in gillnet and purse seine fisheries as well as netting programs throughout their distribution. Specific cases are outlined below:

Unspecified manta rays, likely Reef Manta Ray, caught as non-target species in purse seiners from associated sets in the waters of Papua New Guinea. Catch rates monitored from 1995 until 2006 showed a distinct and significant rise in the number of manta rays caught (both tonnes per annum and kilos per day) in these fisheries in 2001, which steadily rose until 2005/2006, when sharp declines were noticed in the catch (C. Rose pers. comm. 2008). On average, from 1994 until 2006, manta rays comprised 1.8% of non-target catch from the surveyed purse seiners in the waters of Papua New Guinea (C. Rose pers. comm. 2008).

Incidental catches of manta rays in the protective shark nets off the beaches of KwaZulu-Natal, South Africa, peak in the summer months (49% of the total annual catch), although the species is caught throughout the year (Young 2001). Manta rays comprised 16.9% of the total historical batoid catches from these nets, with a mean annual catch of 60 individuals and an overall 33.7% mortality rate (Young 2001).

United States: In 2009, the Governor of Hawaii signed House Bill 366 creating Act 092(09) establishing criminal penalties and administrative fines for knowingly killing or capturing manta rays within State waters. This makes Hawaii the first state in the US union to protect manta rays. There have never been fisheries for manta rays in Hawaii, but this Bill will protect all Manta species living in or passing through the island group from future fishing pressure.

Republic of Maldives: Since June 1995, there has been an export ban on all ray species and their body parts, effectively preventing any commercial fisheries from arising in this country which has never targeted manta rays for local use in significant numbers. Furthermore, in June 2009 the Maldivian Government announced the creation of two new marine protected areas (MPAs), specifically identified for protection because of their importance as areas of critical habitats for the Maldives population of Reef Manta Ray and the occasional transient Giant Manta Ray.

Philippines: Fishing of manta rays was banned in 1998, but this ban was lifted in 1999 due to pressure from fishermen and lack of data on the fishery. During a year-long survey, from March 2002 to March 2003, 156 manta rays (the Giant Manta Ray) were caught, mostly in the months from November to January. Since the study, the ban has been re-established for manta rays, which would offer protection to both species. Mantas are now reported to be rare in the Philippines, especially around the Bohol Sea where the fishery was focused.

Yap: A MPA for manta rays has been created in Yap under the approval of Governor Sebastian Anefal. The sanctuary, which covers 8,234 square miles, taking in 16 islands and 145 islets and atolls, out to 12 miles offshore, will protect the Reef Manta Ray from being targeted by fishermen.

Western Australia: Manta rays whilst not targeted, are protected from any fishing (Fisheries Act) and disturbance or harassment (DEC Act) within marine parks only.

Ito, T. and Kashiwagi, T. 2010. Morphological and genetic identification of two species of manta ray occuring in Japanese waters: Manta birostris and M. alfredi. Report of Japanese Society for Elasmobranch Studies 46: 8-10.

Marshall, A.D., Pierce, S.J. and Bennett, M.B. 2008. Morphological measurements of manta rays (Manta birostris) with a description of a foetus from the east coast of Southern Africa. Zootaxa 1717: 24-30.